Field of the Invention
The present disclosure relates to a nitride semiconductor element formed by crystal growth from a substrate, and a method for manufacturing the same.
Description of the Related Art
Alight emitting diode (LED) made of a nitride semiconductor is normally formed by sequentially stacking an n-type semiconductor layer, an active layer, and a p-type semiconductor layer on a sapphire substrate. Conventionally, there is proposed a means for forming projections on the sapphire substrate in order to improve the light extraction efficiency. In order to suppress deterioration of crystallinity and the occurrence of voids during the crystal growth of a nitride semiconductor on the sapphire substrate with the projections formed thereon, the technique is proposed which involves forming an inclined surface of the projection as a crystal growth suppression surface to promote the growth of the nitride semiconductor in the lateral direction (see WO 2012/002240 A).
It is desirable that the shape of the bottom surface of the projection has a shape close to a regular hexagonal shape from the view point of good growth of the nitride semiconductor having a hexagonal crystal. However, in the technique proposed in WO 2012/002240 A, the bottom surface of the projection is formed in a substantially triangle shape, which does not sufficiently correspond to the growth of the nitride semiconductor, making it difficult for the nitride semiconductor to be grown in some cases. For this reason, the technique proposed in WO 2012/002240 A is desired to further improve an etching method and the shape of the projection.
In a growth process of a GaN-based nitride semiconductor on a sapphire substrate, when crystals of the nitride semiconductor are grown, a buffer layer made of AlGaN and the like is inserted between the sapphire substrate and the nitride semiconductor for the purpose of the relaxation of a lattice mismatch between the sapphire substrate and the nitride semiconductor. When a sapphire substrate with projections formed thereon is used, the nitride semiconductor might be grown from a certain portion of the projection (abnormal growth) in some cases.
The nitride semiconductor is grown from the c-plane of the sapphire substrate ([0001] plane, or an upper surface of the sapphire substrate) not only in the vertical direction, but also in the lateral direction so as to cover the projections. The abnormal growth of the nitride semiconductor from the certain portion of the projection can adversely affect the growth in the lateral direction of the nitride semiconductor. As a result, the obtained nitride semiconductor might have a deteriorated crystallinity.